OLED Device and Preparation Method Thereof, Display Substrate and Display Apparatus

ABSTRACT

Provided is an OLED device, which includes a first electrode, a second electrode, and a first light emitting unit located between the first electrode and the second electrode. An absorption rate of the first electrode for blue light is greater than an absorption rate of the first electrode for red light, and the absorption rate of the first electrode for blue light is greater than an absorption rate of the first electrode for green light. The first light emitting unit includes a light emitting layer and a hole functional unit located between the first electrode and the light emitting layer. The hole functional unit at least includes at least two hole functional layers, and any hole functional layer includes a second functional layer for injecting holes and a third functional layer for transporting holes which are stacked along a direction away from the first electrode.

The present application claims the priority of Chinese patent application No. 202011045684.9, filed to the CNIPA on Sep. 28, 2020 and entitled “OLED Device and Preparation Method Thereof, Display Substrate and Display Apparatus”, the content of which should be regarded as being incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to, but is not limited to, the technical field of display, in particular to an OLED (Organic Light Emitting Diode) device and a preparation method thereof, a display substrate and a display apparatus.

BACKGROUND

Organic Light Emitting Diode (OLED) device has advantages such as ultra-thinness, large viewing angle, active light emission, high brightness, continuous and adjustable color of emitted light, low cost, fast response, low power consumption, wide operating temperature range and flexible display, and have gradually become a promising next generation display technology. In recent years, a lot of research and development work has laid a solid foundation for a large-scale application of OLED device. At present, related OLED display and lighting products have appeared in the market. However, although the manufacturing technology of OLED device is mature, the performance of OLED device is still a key problem that restricts its large-scale application.

SUMMARY

The following is a summary of subject matter described in detail herein. This summary is not intended to limit the protection scope of the claims.

Embodiments of the present disclosure provide an OLED device and a preparation method thereof, a display substrate and a display apparatus.

In an aspect, embodiments of the present disclosure provide an OLED device including a first electrode, a second electrode, and a first light emitting unit located between the first electrode and the second electrode. An absorption rate of the first electrode for blue light is greater than an absorption rate of the first electrode for red light, and the absorption rate of the first electrode for blue light is greater than an absorption rate of the first electrode for green light. The first light emitting unit includes a light emitting layer and a hole functional unit located between the first electrode and the light emitting layer. The hole functional unit includes at least two hole functional layers, and any hole transporting layer includes a second functional layer for injecting holes and a third functional layer for transporting holes, which are stacked along a direction away from the first electrode.

In some exemplary embodiments, a work function of the first electrode ranges from 4.7 eV to 5.2 eV.

In some exemplary embodiments, a difference between a lowest unoccupied molecular orbital (LUMO) energy level of the second functional layer adjacent to the first electrode and the work function of the first electrode is smaller than 1.6 eV.

In some exemplary embodiments, a roughness of the first electrode ranges from 0.6 nm to 1.8 nm.

In some exemplary embodiments, a material of the first electrode includes Titanium Nitride (TiN).

In some exemplary embodiments, the first electrode is in direct contact with a second functional layer of one of the hole functional layers.

In some exemplary embodiments, a thickness of the second functional layer is smaller than a thickness of the third functional layer.

In some exemplary embodiments, a thickness of a second functional layer in a hole functional layer close to the first electrode is smaller than a thickness of a second functional layer in a hole functional layer away from the first electrode in the hole functional unit.

In some exemplary embodiments, a thickness of a third functional layer in a hole functional layer close to the first electrode is smaller than a thickness of a third functional layer in a hole functional layer away from the first electrode in the hole functional unit.

In some exemplary embodiments, a thickness of a second functional layer and a third functional layer may range from 30 angstroms to 1000 angstroms.

In some exemplary embodiments, a light emitting layer includes a first light emitting layer, a second light emitting layer and a third light emitting layer which are sequentially stacked along the direction away from the first electrode, wherein the first light emitting layer and the second light emitting layer are in direct contact with each other, and a connection layer is disposed between the second light emitting layer and the third light emitting layer.

In some exemplary embodiments, the first light emitting layer is a red light emitting layer, the second light emitting layer is a green light emitting layer, and the third light emitting layer is a blue light emitting layer.

In some exemplary embodiments, the hole functional unit further includes a first functional layer for transporting electrons, which is located between the first electrode and the at least two hole functional layers and is in contact with the first electrode. The first functional layer includes an electron transporting material doped with one or more of active metals and active metal compounds. An energy level difference between a lowest unoccupied molecular orbital (LUMO) energy level of the second functional layer and a highest occupied molecular orbital (HOMO) energy level of the third functional layer is smaller than 1 eV.

In some exemplary embodiments, thicknesses of the first functional layer, the second functional layer, and the third functional layer all range from 0.1 nm to 100 nm.

In some exemplary embodiments, a doping ratio of one or more of active metals and active metal compounds doped in the first functional layer ranges from 0.1% to 30%.

In some exemplary embodiments, a LUMO energy level of the first functional layer ranges from 2.0 eV to 3.0 eV, and a HOMO energy level of the first functional layer ranges from 4.5 eV to 7.0 eV.

In some exemplary embodiments, the LUMO energy level of the second functional layer ranges from 4.5 eV to 8.0 eV, and the HOMO energy level of the third functional layer ranges from 4.5 eV to 8.0 eV.

In some exemplary embodiments, the hole functional layer further includes a fourth functional layer located between the second functional layer and the third functional layer, and the fourth functional layer is a mixed layer including a hole injection material and a hole transporting material. An energy level difference between a HOMO energy level of the hole transporting material of the fourth functional layer and the LUMO energy level of the second functional layer is smaller than 1 eV, and an energy level difference between the HOMO energy level of the hole transporting material of the fourth functional layer and the HOMO energy level of the third functional layer is smaller than 1 eV.

In some exemplary embodiments, a doping ratio of the hole injection material of the fourth functional layer in the fourth functional layer ranges from 0.1% to 20%.

In some examples, the hole injection material of the fourth functional layer is the same as a material of the second functional layer, and the hole transporting material of the fourth functional layer is the same as a material of the third functional layer.

In some exemplary embodiments, the first functional layer includes a first material layer in contact with the first electrode and a second material layer between the first material layer and the hole functional layer; the first material layer includes a metal material, and the second material layer includes an electron transporting material doped with one or more of an active metal and an active metal compound.

In some exemplary embodiments, the first light emitting unit further includes at least one of a hole transporting layer between the hole functional unit and the light emitting layer, an electron blocking layer between the light emitting layer and the hole transporting layer, an electron blocking layer between the light emitting layer and the hole functional unit, an electron transporting layer between the light emitting layer and the second electrode, an electron injection layer between the electron transporting layer and the second electrode, and a hole blocking layer located between the light emitting layer and the electron transporting layer.

In some exemplary embodiments, the OLED device further includes one or more second light emitting units located between the first light emitting unit and the second electrode; wherein adjacent light emitting units are connected through a connection layer; the first light emitting unit and the second light emitting unit emit light with different colors. At least one of the second light emitting units includes a light emitting layer and at least one of a hole injection layer, a hole transporting layer, an electron blocking layer, an electron transporting layer, an electron injection layer and a hole blocking layer.

In some exemplary embodiments, the first electrode is a reflective anode and the second electrode is a light-transmitting cathode.

In another aspect, one embodiment of the present disclosure provides a display substrate including the OLED device described above.

In another aspect, an embodiment of the present disclosure provides a display apparatus, which includes the display substrate described above.

In another aspect, an embodiment of the present disclosure provides a preparation method of an OLED device, which includes: forming a first electrode, a first light emitting unit and a second electrode on a substrate. An absorption rate of the first electrode for blue light is greater than an absorption rate of the first electrode for red light, and the absorption rate of the first electrode for blue light is greater than an absorption rate of the first electrode for green light. The forming a first light emitting unit includes: sequentially forming a hole functional unit and a light emitting layer; a hole functional unit is formed, including: forming at least two hole functional layers on a side of the first electrode away from the substrate, any hole functional layer includes a second functional layer for injecting holes and a third functional layer for transporting holes which are stacked along a direction away from the first electrode.

In some exemplary embodiments, the first electrode is in direct contact with the second functional layer of one of the hole functional layers in the hole functional unit.

In some exemplary embodiments, the hole functional unit further includes a first functional layer for transporting electrons in contact with the first electrode, and the first functional layer is located between the first electrode and the at least two hole functional layers. The first functional layer includes an electron transporting material doped with one or more of active metals and active metal compounds; an energy level difference between a lowest unoccupied molecular orbital (LUMO) energy level of the second functional layer and a highest occupied molecular orbital (HOMO) energy level of the third functional layer is smaller than 1 eV.

In some exemplary embodiments, the hole functional layer further includes a fourth functional layer located between the second functional layer and the third functional layer, and the fourth functional layer is a mixed layer including a hole injection material and a hole transporting material. An energy level difference between a HOMO energy level of the hole transporting material of the fourth functional layer and the LUMO energy level of the second functional layer is smaller than 1 eV, and an energy level difference between the HOMO energy level of the hole transporting material of the fourth functional layer and the HOMO energy level of the third functional layer is smaller than 1 eV.

Other aspects will be understood after the drawings and the detailed description are read and understood.

BRIEF DESCRIPTION OF DRAWINGS

Accompanying drawings are used to provide a further understanding of technical solutions of the present disclosure and constitute a part of the description to explain the technical solutions of the present disclosure together with embodiments of the present disclosure, and do not constitute any limitation on the technical solutions of the present disclosure. Shapes and sizes of one or more components in the accompanying drawings do not reflect real scales, and are only for a purpose of schematically illustrating contents of the present disclosure.

FIG. 1 is a schematic diagram of a structure of an OLED device according to at least one embodiment of the present disclosure;

FIG. 2 is another schematic diagram of a structure of an OLED device according to at least one embodiment of the present disclosure;

FIG. 3 is a schematic diagram of an energy level of a hole functional unit of an OLED device according to at least one embodiment of the present disclosure;

FIG. 4 is a schematic diagram of a spectrum of an OLED device in Comparative Example 1;

FIG. 5 is a schematic diagram of a spectrum of an OLED device according to Example 1 of at least one embodiment of the present disclosure

FIG. 6 is a comparison diagram of current density-current efficiency (J-CE) curves of an OLED device in Example 1 of at least one embodiment of the present disclosure and an OLED device in Comparative Example 1;

FIG. 7 is a comparison diagram of current density-brightness (J-L) curves of an OLED device in Example 1 of at least one embodiment of the present disclosure and an OLED device in Comparative Example 1;

FIG. 8 is a comparison diagram of life curves of an OLED device in Example 1 of at least one embodiment of the present disclosure and an OLED device in Comparative Example 1;

FIG. 9 is another schematic diagram of a structure of an OLED device according to at least one embodiment of the present disclosure;

FIG. 10 is a schematic diagram of another energy level of a hole functional unit of an OLED device according to at least one embodiment of the present disclosure;

FIG. 11 is a schematic diagram of another structure of an OLED device according to at least one embodiment of the present disclosure;

FIG. 12 is a schematic diagram of another structure of an OLED device according to at least one embodiment of the present disclosure;

FIG. 13 is a spectrum comparison diagram of Comparative Example 2 and Example 2 according to at least one embodiment of the present disclosure;

FIG. 14 is a schematic diagram of a display substrate according to at least one embodiment of the present disclosure;

FIG. 15 is a schematic diagram of a display apparatus according to at least one embodiment of the present disclosure.

DETAILED DESCRIPTION

To make the objects, technical solutions and advantages of the present disclosure more clear, embodiments of the present disclosure will be described in detail below with reference to the drawings. The embodiments may be implemented in a number of different forms. Those of ordinary skills in the art will readily understand the fact that implementations and contents may be transformed into one or more of forms without departing from the spirit and scope of the present disclosure. Therefore, the present disclosure should not be construed as being limited only to what is described in the following embodiments. The embodiments and features in the embodiments in the present disclosure may be combined randomly if there is no conflict.

In the drawings, sizes of one or more constituent elements, or thicknesses or regions of layers, are sometimes exaggerated for clarity. Therefore, an implementation of the present disclosure is not necessarily limited to the sizes shown. The shapes and sizes of various components in the drawings do not reflect true scales. In addition, the drawings schematically show ideal examples, and an implementation of the present disclosure is not limited to the shapes or values shown in the drawings.

The “first”, “second”, “third” and other ordinal numbers in the present disclosure are used to avoid confusion of constituent elements, not to provide any quantitative limitation. In the description of the present disclosure, “multiple” means two or more counts.

In the present disclosure, for the sake of convenience, wordings such as “central”, “upper”, “lower”, “front”, “rear”, “vertical”, “horizontal”, “top”, “bottom”, “inner”, “outer” and the others describing the orientations or positional relations are used to depict relations of elements with reference to the drawings, which are only for an easy and simplified description of the present disclosure, rather than for indicating or implying that the apparatus or element referred to must have a specific orientation, or must be constructed and operated in a particular orientation and therefore, those wordings may not be construed as limitations on the present disclosure. The positional relations of the constituent elements may be appropriately changed according to the direction in which constituent elements are described. Therefore, the wordings are not limited in the specification, and may be replaced appropriately according to situations.

In the present disclosure, the terms “installed”, “connected” and “coupled” shall be understood in their broadest sense unless otherwise explicitly specified and defined. For example, a connection may be a fixed connection, or a detachable connection, or an integrated connection; it may be a mechanical connection, or an electrical connection; it may be a direct connection, or an indirect connection through middleware, or an internal connection between two elements. Those of ordinary skills in the art may understand the specific meanings of the above terms in the present disclosure according to situations.

In the present disclosure, “an electrical connection” includes a case where constituent elements are connected via an element having a certain electrical action. The “element with a certain electric action” is not particularly limited as long as it may transmit and receive electrical signals between the connected constituent elements. Examples of the “element having a certain electrical action” not only include electrodes and wirings, but also include switching elements such as transistors, resistors, inductors, capacitors, and other elements with one or more functions.

In the present disclosure, “parallel” refers to a state in which an angle formed by two straight lines is above −10 degrees and below 10 degrees, and thus may include a state in which the angle is above −5 degrees and below 5 degrees. In addition, “perpendicular” refers to a state in which an angle formed by two straight lines is above 80 degrees and below 100 degrees, and thus may include a state in which the angle is above 85 degrees and below 95 degrees.

“About” in the present disclose means that limits of a value are not limited strictly, and the value is within a range of process and measurement errors.

In this disclosure, “an energy level difference between an energy level A and an energy level B” means an absolute value of a difference between an energy level A and an energy level B.

An OLED device according to at least one embodiment of the present disclosure includes a first electrode, a second electrode, and a first light emitting unit located between the first electrode and the second electrode. An absorption rate of the first electrode for blue light is greater than an absorption rate of the first electrode for red light, and the absorption rate of the first electrode for blue light is greater than an absorption rate of the first electrode for green light. The first light emitting unit includes a light emitting layer and a hole functional unit located between the first electrode and the light emitting layer. The hole functional unit includes at least two hole functional layers. Any hole functional layer includes a second functional layer for injecting holes and a third functional layer for transporting holes, which are stacked along a direction away from the first electrode.

An OLED device according to at least one embodiment of the present disclosure may overcome and improve the difficulty and balance of the hole injection on a surface of the first electrode, thereby improving a light emission consistency of the OLED device by disposing at least two hole functional layers between the first electrode and the light emitting layer.

In some exemplary embodiments, a work function of the first electrode ranges from 4.7 eV to 5.2 eV. For example, the work function of the first electrode may be 5.0 eV. However, this is not limited in the present embodiment.

In some exemplary embodiments, a difference between a lowest unoccupied molecular orbital (LUMO) energy level of the second functional layer adjacent to the first electrode and a work function of the first electrode is smaller than 1.6 eV. For example, the difference between the lowest unoccupied molecular orbital (LUMO) energy level of the second functional layer adjacent to the first electrode and the work function of the first electrode may be 1 eV.

In some exemplary embodiments, a roughness of the first electrode ranges from 0.6 nm to 1.8 nm. In some examples, the first electrode may be a single layer structure and is made of TiN. The roughness of the first electrode may range from 0.6 nm to 0.7 nm, for example, a roughness of TiN is 0.6 nm. In some examples, the first electrode may be a composite structure of Ti/Al/TiN, and the roughness of the first electrode may range from 1.2 nm to 1.8 nm, for example, the roughness of the first electrode may be 1.2 nm. However, this is not limited in the present embodiment.

In some exemplary embodiments, a material of the first electrode may include Titanium Nitride (TiN). For example, the first electrode may be a single layer structure, and is made of TiN; or, the first electrode may be a composite structure of Ti/Al/TiN. However, this is not limited in the present embodiment.

In some exemplary embodiments, the first electrode is in direct contact with the second functional layer of one of the hole functional layers of the hole functional unit.

In some exemplary embodiments, a thickness of the second functional layer in the hole functional unit is smaller than a thickness of the third functional layer in the hole functional unit. However, this is not limited in the present embodiment. For example, the thickness of the second functional layer and the thickness of the third functional layer in the hole functional unit may be the same.

In some exemplary embodiments, a thickness of a second functional layer in a hole functional layer close to the first electrode in the hole functional unit is smaller than a thickness of a second functional layer in a hole functional layer away from the first electrode in the hole functional unit. In other words, thicknesses of the second functional layers in the hole functional unit gradually increases along a direction away from the first electrode. However, this is not limited in the present embodiment. For example, thicknesses of the second functional layers in the hole functional unit may be the same.

In some exemplary embodiments, a thickness of a third functional layer in a hole functional layer close to the first electrode in the hole functional unit is smaller than a thickness of a third functional layer in a hole functional layer away from the first electrode in the hole functional unit. In other words, thicknesses of the third functional layers in the hole functional unit gradually increases along the direction away from the first electrode. However, this is not limited in the present embodiment. For example, thicknesses of the third functional layers in the hole functional unit may be the same.

In some exemplary embodiments, the thickness of the second functional layer and the thickness of the third functional layer may both range from 30 angstroms to 1000 angstroms. For example, the thickness of the second functional layer may be 100 angstroms, and the thickness of the third functional layer may be 300 angstroms. However, this is not limited in the present embodiment.

In some exemplary embodiments, the light emitting layer includes a first light emitting layer, a second light emitting layer and a third light emitting layer which are sequentially stacked along the direction away from the first electrode, wherein the first light emitting layer and the second light emitting layer are in direct contact with each other, and a connection layer is disposed between the second light emitting layer and the third light emitting layer. The first light emitting unit of this example includes the first light emitting layer, the second light emitting layer, and the third light emitting layer which are stacked. However, this is not limited in the present embodiment. In some examples, the first light emitting unit includes only one light emitting layer.

In some exemplary embodiments, the first light emitting layer is a red light emitting layer, the second light emitting layer is a green light emitting layer, and the third light emitting layer is a blue light emitting layer. In other words, the first light emitting unit may emit white light. However, this is not limited in the present embodiment.

In some exemplary embodiments, a hole functional unit at least includes a first functional layer for transporting electrons and at least two hole functional layers between the first functional layer and the light emitting layer. The first functional layer is in contact with the first electrode. Any hole functional layer at least includes a second functional layer for injecting holes and a third functional layer for transporting holes. The first functional layer includes an electron transporting material doped with one or more of active metals and active metal compounds. An energy level difference between a lowest unoccupied molecular orbital (LUMO) energy level of the second functional layer and a highest occupied molecular orbital (HOMO) energy level of the third functional layer is smaller than 1 electron volt (eV). The first electrode may be an anode and the second electrode may be a cathode. In this exemplary embodiment, the energy level difference between the LUMO energy level of the second functional layer and the HOMO energy level of the third functional layer is smaller than 1 eV, and hole-electron pairs are separated under an action of an applied electric field. Among them, electrons flow into the anode through the first functional layer. Since the electron transporting material of the first functional layer is doped with one or more of active metals and active metal oxides, an efficiency of an electron injection and transport of the first functional layer may be improved without being affected by an anode work function. Holes are directly transported to the light emitting layers through the HOMO energy level of the third functional layer. The OLED device according to the present exemplary embodiment may overcome the difficulty of injecting holes from the anode by disposing a hole functional unit between the anode and the light emitting layer, thereby effectively reducing an operating voltage of the OLED device, and reducing a power consumption. Furthermore, the anode of the OLED device of this embodiment is not limited to materials with a high work function (e.g., a work function greater than 5 eV), and a selectable range of anode materials may be expanded (e.g., materials with work function smaller than 5 eV may be selected).

In some exemplary embodiments, the first electrode is a reflective anode and the second electrode is a light-transmitting cathode. In other words, the OLED device of this exemplary embodiment is an OLED device of a top emitting structure. In some examples, an anode may adopt a conductive material with a function of reflected light, such as any one or more metal materials of titanium (Ti), aluminum (Al) and molybdenum (Mo), or a compound of the above metals, such as titanium nitride (TiN). An anode may be a single-layer structure or a multi-layer composite structure, such as Ti/Al/TiN, Ti/Al/Ti, Ti/Al/Ti/Mo and Ti/Al. A conductive material having a function of transmitting light, such as transparent metal oxides such as indium zinc oxide (IZO), or alloys of magnesium (Mg) and silver (Ag), alloys of ytterbium (Yb) and Ag, may be used as a cathode. However, this is not limited in the present embodiment.

In some exemplary embodiments, thicknesses of a first functional layer, a second functional layer and a third functional layer included in a hole functional unit all range from 0.1 nm to 100 nm. In some examples, thicknesses of a first functional layer, a second functional layer and a third functional layer may all range from 10 nm to 50 nm. However, this is not limited in the present embodiment. For example, the first functional layer, the second functional layer and the third functional layer may have different thicknesses according to different needs.

In some exemplary embodiments, a doping ratio of one or more of active metals and active metal compounds doped in the first functional layer ranges from 0.1% to 30%. In other words, the mass of the doped material (i.e., one or more of active metals and active metal compounds) in the first functional layer accounts for 0.1% to 30% of the total mass of the electron transporting material and the doped material in the first functional layer. In some examples, a doping ratio of the doped material in the first functional layer may range from 0.1% to 5%. For example, a doping ratio of the doped material in the first functional layer may be about 5%. However, this is not limited in the present embodiment.

The “doping ratio” in the present disclosure refers to the ratio of the mass of an object material to the total mass of a subject material and the object material.

In some exemplary embodiments, active metals doped in the first functional layer may include basic metals and other highly active metals, such as ytterbium (Yb). The basic metals refer to six metal elements in the periodic table except hydrogen (h), namely lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs) and francium (Fr). The active metal compounds doped in the first functional layer may include basic metal compounds and other highly active metal compounds, such as Yb compounds. In some examples, Li may be doped in an electron transporting material of the first functional layer. However, this is not limited in the present embodiment.

In some exemplary embodiments, the first functional layer may include a first material layer in contact with the first electrode and a second material layer between the first material layer and the hole functional layer. The first material layer includes a metal material, and the second material layer includes an electron transporting material doped with one or more of an active metal and an active metal compound. In this exemplary embodiment, the first functional layer may be a multilayer structure. However, this is not limited in the present embodiment. In some examples, the first functional layer may be a single layer structure.

In some exemplary embodiments, a LUMO energy level of the first functional layer ranges from 2.0 eV to 3.0 eV, and a HOMO energy level of the first functional layer ranges from 4.5 eV to 7.0 eV.

In some exemplary embodiments, the LUMO energy level of the second functional layer ranges from 4.5 eV to 8.0 eV, and the HOMO energy level of the third functional layer ranges from 4.5 eV to 8.0 eV. In some examples, the HOMO energy level of the third functional layer ranges from 4.5 eV to 6.0 eV. However, this is not limited in the present embodiment.

The OLED device according to this embodiment will be illustrated below through a number of examples. In the following example, the first electrode is an anode and the second electrode is a cathode.

FIG. 1 is a schematic diagram of a structure of an OLED device according to at least one embodiment of the present disclosure. As shown in FIG. 1, the OLED according to this this exemplary embodiment includes an anode 100, a cathode 300, and a first light emitting unit 200 located between the anode 100 and the cathode 300. An absorption rate of the anode 100 for blue light is greater than an absorption rate of the anode 100 for red light, and the absorption rate of the anode 100 for blue light is greater than an absorption rate of the anode 100 for green light. The first light emitting unit 200 includes a hole functional unit 210 and a light emitting layer 220 which are sequentially stacked along a direction away from the anode 100. The hole functional unit 210 is located between the anode 100 and the light emitting layer 220, and the hole functional unit 210 is in contact with the anode 100. The hole functional unit 210 includes two hole functional layers sequentially stacked along the direction away from the anode 100. One hole functional layer is in contact with the anode 100, and the other hole functional layer is in contact with the light emitting layer 220. The hole functional layer close to the anode 100 includes a second functional layer 212 a and a third functional layer 213 a sequentially stacked, and the hole functional layer away from the anode 100 includes a second functional layer 212 b and a third functional layer 213 b sequentially stacked. In this example, the hole functional unit 210 includes a second functional layer 212 a, a third functional layer 213 a, a second functional layer 212 b, and a third functional layer 213 b which are sequentially stacked along the direction away from the anode 100. However, this is not limited in the present embodiment. For example, the hole functional unit may include three or more stacked hole functional layers.

In some examples, the anode 100 may be a composite structure of Ti/Al/TiN. In some examples, a thickness of Ti is about 20 nanometers (nm), a thickness of Al is about 70 nm, and a thickness of TiN ranges from about 10 nm to 20 nm. For example, a thickness of TiN may be about 15 nm. However, this is not limited in the present embodiment. In some examples, the anode 100 may be a composite structure of Ti/Al/Ti or ITO (Indium Tin Oxide)/Ag/ITO. For example, a thickness of Ti is about 20 nanometers (nm), and a thickness of Al is about 70 nm. For example, a thickness of Ag is about 100 nm, and a thickness of ITO layer is about 10 nm.

In some examples, the cathode 300 may be made of an alloy material of silver (Ag) and magnesium (Mg). For example, mass of Mg accounts for about 15% of total mass of the alloy.

In some examples, the second functional layers 212 a and 212 b may be made of hole injection materials such as HATCN (Dipyrazino[2,3-f:2′,3′-h]quinoxaline-2,3,6,7,10,11-hexacarbonitrile; 2,3,6,7,10,11-hexacyano-1,4,5,8,9,12-hexaazatriphenylene), LG101, or F4-TCNQN. The third functional layers 213 a and 213 b may be made of NPB(N,N′-bis(naphthalen-1-yl)-N,N′-bis(phenyl)-benzidine; N,N′-diphenyl-N,N′-(1-naphthyl)-1,1′-Biphenyl-4,4′-diamine (123847-85-8)). Thickness ranges of the second functional layers 212 a and 212 b and the third functional layers 213 a and 213 b may be 30 angstroms to 1000 angstroms. For example, thicknesses of the second functional layers 212 a and 212 b may be about 100 angstroms, and thicknesses of the third functional layers 213 a and 213 b may be about 300 angstroms. However, this is not limited in the present embodiment.

In some examples, taking the light emitting layer 220 being a blue light emitting layer as an example, the light emitting layer 220 may use MAND(2-methyl-9,10-bis(naphthalen-2-yl)anthracene) as a blue light emitting material. Light emitting materials may be undoped or may be doped. For example, DSA-Ph (1-4-di-[4-(N,N-diphenyl)amino]styryl-benzene; 1,4-bis[4-(dimet-tolylamino)styryl]benzene) may be doped in MAND with a doping ratio of about 5%. A material of the light emitting layer 220 may be selected to emit red light (R), green light (G) and blue light (B) according to needs, or light emitting materials may be doped according to actual needs, and a doping object may be a material that helps to emit corresponding fluorescence or phosphorescence. However, this is not limited in the present embodiment.

FIG. 2 is a schematic diagram of another structure of an OLED device according to at least one embodiment of the present disclosure. As shown in FIG. 2, the OLED device according to this exemplary embodiment includes an anode 100, a cathode 300, and a first light emitting unit 200 located between the anode 100 and the cathode 300. The first light emitting unit 200 includes a hole functional unit 210, a first light emitting layer 220 a, a second light emitting layer 220 b, a connection layer 700, a third light emitting layer 220 c, an electron transporting layer 250 and an electron injection layer 260 which are sequentially stacked. The hole functional unit 210 is located between the anode 100 and the first light emitting layer 220 a; the second light emitting layer 220 b is located between the first light emitting layer 220 a and the connection layer 700; the connection layer 700 is located between the second light emitting layer 220 b and the third light emitting layer 220 c; the third light emitting layer 220 c is located between the connection layer 700 and the electron transporting layer 250; and the electron injection layer 260 is located between the electron transporting layer 250 and the cathode 300. The hole functional unit 210 includes a second functional layer 212 a, a third functional layer 213 a, a second functional layer 212 b, and a third functional layer 213 b which are sequentially stacked. In other words, the hole functional unit 210 includes two stacked hole functional layers. The second functional layer 212 a is in direct contact with the anode 100. In some examples, the anode 100 may be a composite structure of Ti/Al/TiN. Among them, a roughness of TiN ranges from 0.6 nm to 0.7 nm, for example, the roughness of TiN is 0.6 nm. A work function of TiN ranges from 4.7 eV to 5.2 eV. A difference between a LUMO energy level of the second functional layer adjacent to the anode 100 and the work function of TiN of the anode 100 is smaller than 1.6 eV. In some examples, the LUMO energy level of the second functional layer ranges from 5 eV to 6 eV, and a HOMO energy level of the second functional layer ranges from 9.5 eV to 10 eV. A LUMO energy level of the third functional layer ranges from 2.0 eV to 2.7 eV, and the HOMO energy level of the third functional layer ranges from 5.2 eV to 5.7 eV. An energy level difference between the LUMO energy level of the second functional layer and the HOMO energy level of the third functional layer is smaller than 0.2 eV.

In some examples, thicknesses of the third functional layers 213 a and 213 b are both greater than thicknesses of the second functional layers 212 a and 212 b. A thickness of the second functional layer 212 b is greater than a thickness of the second functional layer 212 a. A thickness of the third functional layer 213 b is greater than a thickness of the third functional layer 213 a. In other words, in the hole functional unit 210, the thickness of the second functional layer 212 a is smaller than the thickness of the second functional layer 212 b; the thickness of the second functional layer 212 b is smaller than that of the third functional layer 213 a; and the thickness of the third functional layer 213 a is smaller than the thickness of the third functional layer 213 b. However, this is not limited in the present embodiment. For example, thicknesses of multiple second functional layers and thickness of multiple third functional layers in the hole functional unit are the same.

In some examples, the first light emitting layer 220 a may be a red light emitting layer, the second light emitting layer 220 b may be a green light emitting layer, and the third light emitting layer 220 c may be a blue light emitting layer. The first light emitting unit 200 may emit white light. However, this is not limited in the present embodiment. For example, the first light emitting unit may emit light of other colors.

In some examples, the electron transporting layer 250 may be made of Bphen, and a thickness of the electron transporting layer 250 is about 35 nm. The electron injection layer 260 is made of Bphen doped with LiQ (the doping ratio is 10%), and a thickness of the electron injection layer 260 is about 80 nm. However, this is not limited in the present embodiment.

FIG. 3 is a schematic diagram of an energy level of a hole functional unit of an OLED device according to at least one embodiment of the present disclosure. As shown in FIG. 3, carriers transported into the first light emitting layer 220 a undergo multiple hole-electron balances of the hole functional unit 210, so that the holes transported to the first light emitting layer 220 a become balanced, and stable hole transporting from the anode 100 to the first light emitting layer 220 a is realized. In this example, through two groups of hole injecting and transporting functional layers in the hole functional unit between the anode and the light emitting layer, the multiple hole-electron balances may be performed in the carrier transporting to provide the stable hole transporting to the light emitting layer, thereby overcoming and improving the difficulty and balance of the anode hole injection.

Next, performances of an OLED device in Example 1 and an OLED device in Comparative Example 1 will be compared. For example, the structure shown in FIG. 2 is adopted in the OLED device in Example 1. A difference between the structure of the OLED device in Comparative Example 1 and that of the OLED device in Example 1 is that the OLED device in Comparative Example 1 does not include a hole functional unit, but a conventional hole injection layer and a hole transporting layer are disposed between the anode and the first light emitting layer.

In Comparative Example 1, the OLED device may be formed on a silicon-based substrate. The anode may be a composite structure of Ti/Al/TiN. A cathode may be made of an alloy material of Ag and Mg, wherein mass of Mg accounts for about 15% of total mass of the alloy; a thickness of the cathode is about 10 nm. There is a hole injection layer, a hole transporting layer, a first light emitting layer, a second light emitting layer, a connection layer, a third light emitting layer, an electron transporting layer and an electron injection layer between the anode and the cathode in sequence.

Materials and thicknesses of the substrate, anode, cathode, first light emitting layer, second light emitting layer, connection layer, third light emitting layer, electron injection layer and electron transporting layer in Example 1 are the same as those in Comparative Example 1. Materials of the two second functional layers in Example 1 may be the same as those of the hole injection layer in Comparative Example 1, and materials of the two third functional layers may be the same as those of the hole transporting layer in Comparative Example 1.

FIG. 4 is a schematic diagram of a spectrum of an OLED device in Comparative Example 1. FIG. 5 is a schematic diagram of a spectrum of an OLED device according to Example 1 according to at least one embodiment of the present disclosure. In FIG. 4 and FIG. 5, lines with different shapes represent spectral changes of the OLED device under different voltages. As shown in FIG. 4, in the OLED device in Comparative Example 1, holes are directly injected from the anode and transported to the first light emitting layer through the hole injection layer and the hole transporting layer. Under low voltage, light emissions of the green light (wavelength range is about 492 nm to 577 nm) and the blue light (wavelength range is about 400 nm to 450 nm) are weak, while under high voltage, light emissions of the green light and the blue light are enhanced. It may be seen that spectral consistency of the OLED device in Comparative Example 1 is poor. As shown in FIG. 5, the OLED device in Example 1 has better spectral consistency under different voltages, and ratios of the blue light, the red light and the green light in the white light spectrum will not change with voltage changes. The spectrum of the OLED device in Example 1 is less affected by the voltage.

FIG. 6 is a comparison diagram of current density-current efficiency (J-CE) curves of an OLED device in Example 1 of the present disclosure and an OLED device in Comparative Example 1. In FIG. 6, the abscissa represents a current density of the device and the ordinate represents an efficiency of the device. As shown in FIG. 6, when the current density is greater than 20 mA*cm⁻², the current efficiency of the OLED device in Example 1 is higher than that of the OLED device in Comparative Example 1. It may be seen that a brightness of the OLED device in Example 1 is higher than that of the OLED device in Comparative Example 1. Under a same brightness, the OLED device in Example 1 has a low current density and a long service life.

FIG. 7 is a comparison diagram of current density-brightness (J-L) curves of an OLED device in Example 1 of at least one embodiment of the present disclosure and an OLED device in Comparative Example 1. In FIG. 7, the abscissa represents a current density of the device and the ordinate represents the brightness in cd/m². As shown in FIG. 7, under a same current density, a brightness of the OLED device in Example 1 is higher than that of the OLED device in Comparative Example 1. Under a same brightness, the OLED device in Example 1 has a low current density and a long service life.

FIG. 8 is a comparison diagram of life curves of an OLED device in Example 1 of at least one embodiment of the present disclosure and an OLED device in Comparative Example 1. In FIG. 8, the abscissa represents time, and the ordinate represents the percentage of brightness relative to an initial brightness. As shown in FIG. 8, a service life of the OLED device in Example 1 compared with the OLED device in Comparative Example 1 is longer, and the service life of the OLED device in Example 1 may be increased by about 1.8 times.

In some exemplary embodiments, the hole functional unit may further include a first functional layer that transports electrons in contact with the first electrode. The first functional layer is located between the first electrode and the hole functional layer. The first functional layer includes an electron transporting material doped with one or more of active metals and active metal compounds. An energy level difference between a LUMO energy level of the second functional layer and a HOMO energy level of the third functional layer of the hole functional layer is smaller than 1 eV.

In some examples, when the hole functional unit includes a first functional layer and multiple hole functional layers, the number of functional layers included in different hole functional layers may be the same or different. For example, the hole functional unit may include a first functional layer and three hole functional layers, and each hole functional layer may include a second functional layer and a third functional layer which are stacked.

In some examples, when the hole functional unit includes a first functional layer and multiple hole functional layers, materials of second functional layers in different hole functional layers may be the same, or materials of third functional layers in different hole functional layers may be the same. However, this is not limited in the present embodiment. In some examples, when a hole functional unit includes a first functional layer and multiple hole functional layers, materials of second functional layers in different hole functional layers may be different, or materials of third functional layers in different hole functional layers may be the different.

In some examples, when a hole functional unit includes a first functional layer and multiple hole functional layers, thicknesses of second functional layers in different hole functional layers may be the same, or thicknesses of third functional layers in different hole functional layers may be the same; or thicknesses of fourth functional layers in different hole functional layers may be the same. However, this is not limited in the present embodiment. In some examples, when a hole functional unit includes a first functional layer and multiple hole functional layers, thicknesses of second functional layers in different hole functional layers may be different, or thicknesses of third functional layers in different hole functional layers may be different; or thicknesses of fourth functional layers in different hole functional layers may be different.

FIG. 9 is a schematic diagram of another structure of an OLED device according to at least one embodiment of the present disclosure. As shown in FIG. 9, the OLED device according to the present exemplary embodiment includes an anode 100, a cathode 300, and a first light emitting unit 200 located between the anode 100 and the cathode 300. The first light emitting unit 200 includes: a hole functional unit 210, a hole transporting layer 230, an electron blocking layer 240, a light emitting layer 220, an electron transporting layer 250, and an electron injection layer 260 that are sequentially stacked. The hole functional unit 210 is located between the anode 100 and the hole transporting layer 230, the electron blocking layer 240 is located between the hole transporting layer 230 and the light emitting layer 220, the electron transporting layer 250 is located between the light emitting layer 220 and the electron injection layer 260, and the electron injection layer 260 is located between the electron transporting layer 250 and the cathode 300. The hole functional unit 210 includes a first functional layer 211 for transporting electrons and two hole functional layers that are sequentially stacked. A hole functional layer close to the anode 100 includes a second functional layer 212 a for injecting holes and a third functional layer 213 a for transporting holes which are stacked. A hole functional layer away from the anode 100 includes a second functional layer 212 b for injecting holes and a third functional layer 213 b for transporting holes which are stacked. In the present exemplary embodiment, the hole functional unit 210 includes a first functional layer 211, a second functional layer 212 a, a third functional layer 213 a, a second functional layer 212 b, and a third functional layer 213 b which are sequentially stacked. However, this is not limited in the present embodiment. In some examples, the hole functional unit may include three or more hole functional layers.

In some exemplary embodiments, the anode 100 may be a composite structure of Ti/Al/Ti or ITO/Ag/ITO or Ti/Al/TiN. In some examples, a thickness of Ti is about 20 nanometers (nm), and a thickness of Al is about 70 nm. In some examples, a thickness of Ag is about 100 nm, and a thickness of ITO layer is about 10 nm. The cathode 300 may be made of an alloy material of Ag and Mg, wherein mass of Mg accounts for about 15% of total mass of the alloy. In some examples, an electron transporting material of the first functional layer 211 may be Bphen (4,7-diphenyl-1,10-phenanthroline; 4,7-diphenyl o-phenanthroline). The electron transporting material of the first functional layer 211 may be doped with Li or LIQ (lithium 8-hydroxyquinoline). The second functional layers 212 a and 212 b may be made of hole injection materials such as HATCN (Dipyrazino[2,3-f:2′,3′-h]quinoxaline-2,3,6,7,10,11-hexacarbonitrile; 2,3,6,7,10,11-hexacyano-1,4,5,8,9,12-hexaazatriphenylene), LG101, or F4-TCNQN. The third functional layers 213 a and 213 b may be made of NPB (N,N′-bis(naphthalen-1-yl)-N,N′-bis(phenyl)-benzidine; N,N′-diphenyl-N,N′-(1-naphthyl)-1,1′-Biphenyl-4,4′-diamine (123847-85-8)). Thickness ranges of the first functional layer 211, the second functional layers 212 a and 212 b, and the third functional layers 213 a and 213 b may all be 10 nm to 50 nm.

In some exemplary embodiments, taking the light emitting layer 220 being a blue light emitting layer as an example, the light emitting layer 220 may use MAND(2-methyl-9,10-bis(naphthalen-2-yl)anthracene) as a blue light emitting material. Light emitting materials may be undoped or may be doped. For example, DSA-Ph (1-4-di-[4-(N,N-diphenyl)amino]styryl-benzene; 1,4-bis[4-(dimet-tolylamino)styryl]benzene) may be doped in MAND with a doping ratio of about 5%. A material of the light emitting layer 220 may be selected to emit red light (R), green light (G) and blue light (B) according to needs, or light emitting materials may be doped according to actual needs, and a doping object may be a material that helps to emit corresponding fluorescence or phosphorescence. However, this is not limited in the present embodiment.

In some exemplary embodiments, an electron transporting material of the first functional layer 211 may be the same as or different from a material of the electron transporting layer 250. For example, both materials of the first functional layer and the electron transporting layer may be Bphen. A material of the second functional layer may be HATCN. Materials of the third functional layers 213 a and 213 b may be the same as or different from a material of the hole transporting layer 230. For example, materials of the third functional layer and the hole transporting layer may be NPB. A material of the electron blocking layer may be DBTPB(N4,N4′-bis(dibenzo[b,d]thiophen-4-yl)-N4,N4′-diphenylbiphenyl-4,4′-diaMine). A material of the electron injection layer 260 may be LiQ or Bphen doped with LiQ. In some examples, a doping ratio of LiQ in the electron injection layer may range from 0.1% to 60%, for example, a doping ratio may be 10%.

In some exemplary embodiments, taking the light emitting layer 220 being a blue light emitting layer as an example, a doping subject of the light emitting layer 220 is MAND, a doping object of the light emitting layer 220 is DSA-Ph, and a doping ratio is 5%. In this exemplary embodiment, the anode 100 is a composite structure of Ti/Al/Ti, wherein a thickness of Ti is 20 nm and a thickness of Al is 70 nm. The cathode 300 may be made of an alloy material of Ag and Mg, wherein mass of Mg accounts for about 15% of total mass of the alloy; a thickness of the cathode is about 10 nm. The first functional layer 211 has a doping subject of Bphen, a doping object of Li, and a doping ratio of about 5%. A thickness of the first functional layer 211 is about 20 nm. A material of the second functional layer 212 of the hole functional unit 210 is HATCN, and a thickness of the second functional layer 212 is about 10 nm. A material of the third functional layer 213 of the hole functional unit 210 is NPB, and a thickness of the third functional layer 213 is about 10 nm. A material of the hole transporting layer 230 is NPB, and a thickness of the hole transporting layer 230 is about 80 nm. A material of the electron blocking layer 240 is DBTPB, and a thickness of the electron blocking layer 240 is about 4 nm. A material of the light emitting layer 220 is MAND: DSA-Ph (5%), and a thickness of the light emitting layer 230 is about 20 nm. A material of the electron transporting layer 250 is Bphen, and a thickness of the electron transporting layer 250 is about 35 nm. A material of the electron injection layer 260 is Bphen doped with LiQ (the doping ratio is 10%), and a thickness of the electron injection layer 260 is about 80 nm. In this exemplary embodiment, a material of the hole transporting layer 230 is the same as a material of the third functional layer 213.

FIG. 10 is a schematic diagram of an energy level of a hole functional unit of an OLED device according to the exemplary embodiment. As shown in FIG. 10, a work function of Ti used for the anode 100 is about 4.3 eV. In any hole functional layer, a LUMO energy level of the second functional layer 212 a (or the second functional layer 212 b) is 5.7 eV, and a HOMO energy level of the third functional layer 213 a (or the third functional layer 213 b) is 5.5 eV. In any hole functional layer, an energy level difference (e.g., 0.2 eV) between the LUMO level (e.g., 5.7 eV) of the second functional layer 212 a (or second functional layer 212 b) and the HOMO level (e.g., 5.5 eV) of the third functional layer 213 a (or third functional layer 213 b) is smaller than 1 eV. Hole-electron pairs at interfaces between the second functional layer 212 a (or the second functional layer 212 b) and the third functional layer 213 a (or the third functional layer 213 b) are separated under an action of an applied electric field. In a whole hole functional unit, electrons are transported to the anode and holes are transported to the light emitting layer. The exemplary embodiment may overcome the difficulty of injecting holes into the anode, effectively reduce an operating voltage of OLED device, and expand a selectable range of anode materials (for example, materials with work function smaller than 5 eV may be selected).

In some exemplary embodiments, at least one hole functional layer may further include a fourth functional layer located between the second functional layer and the third functional layer, and the fourth functional layer is a mixed layer including a hole injection material and a hole transporting material. An energy level difference between a HOMO energy level of the hole transporting material of the fourth functional layer and a LUMO energy level of the second functional layer is smaller than 1 eV, and an energy level difference between the HOMO energy level of the hole transporting material of the fourth functional layer and a HOMO energy level of the third functional layer is smaller than 1 eV. In some examples, a hole injection material of the fourth functional layer is the same as a material of the second functional layer, and a hole transporting material of the fourth functional layer is the same as a material of the third functional layer. However, this is not limited in the present embodiment. In some examples, a hole injection material of the fourth functional layer may be different from a material of the second functional layer, or a hole transporting material of the fourth functional layer may be different from a material of the third functional layer.

In some exemplary embodiments, a doping ratio of the hole injection material of the fourth functional layer in the fourth functional layer ranges from 0.1% to 20%. In some examples, the doping ratio of the hole injection material in the fourth functional layer is about 2%. However, this is not limited in the present embodiment.

In some examples, when a hole functional unit includes a first functional layer and multiple hole functional layers, the number of functional layers included in different hole functional layers may be the same or different. For example, a hole functional unit may include a first functional layer and two hole functional layers, one hole functional layer may include a second functional layer, a fourth functional layer and a third functional layer which are stacked, and the other hole functional layer may include a second functional layer and a third functional layer which are stacked.

In some examples, when a hole functional unit includes a first functional layer and multiple hole functional layers, materials of the second functional layers in different hole functional layers may be the same or different, or materials of the third functional layers in different hole functional layers may be the same or different, or materials of the fourth functional layers in different hole functional layers may be the same or different. Thicknesses of the second functional layers in different hole functional layers may be the same or different, or thicknesses of the third functional layers in different hole functional layers may be the same or different, or thicknesses of the fourth functional layers in different hole functional layers may be the same or different. However, this is not limited in the present embodiment.

FIG. 11 is a schematic diagram of another structure of an OLED device according to at least one embodiment of the present disclosure. As shown in FIG. 11, the OLED device according to this exemplary embodiment includes an anode 100, a cathode 300, and a first light emitting unit 200 located between the anode 100 and the cathode 300. The first light emitting unit 200 includes: a hole functional unit 210, a hole transporting layer 230, an electron blocking layer 240, a light emitting layer 220, an electron transporting layer 250, and an electron injection layer 260 that are sequentially stacked. The hole functional unit 210 is located between the anode 100 and the hole transporting layer 230, the electron blocking layer 240 is located between the hole transporting layer 230 and the light emitting layer 220, the electron transporting layer 250 is located between the light emitting layer 220 and the electron injection layer 260, and the electron injection layer 260 is located between the electron transporting layer 250 and the cathode 300. The hole functional unit 210 includes a first functional layer 211 for transporting electrons and two hole functional layers stacked in sequence. One of the hole functional layers includes a second functional layer 212 a for injecting holes, a fourth functional layer 214 and a third functional layer 213 a for transporting holes which are stacked. And the other hole functional layer includes a second functional layer 212 b and a third functional layer 213 b which are stacked. In this exemplary embodiment, the hole functional unit 210 includes a first functional layer 211, a second functional layer 212 a, a fourth functional layer 214, a third functional layer 213 a, a second functional layer 212 b, and a third functional layer 213 b which are sequentially stacked. However, this is not limited in the present embodiment. In some examples, a hole functional unit may include three or more hole functional layers.

In some exemplary embodiments, taking the light emitting layer 220 being a blue light emitting layer as an example, a doping subject of the light emitting layer 220 is MAND, a doping object of the light emitting layer 220 is DSA-Ph, and a doping ratio is 5%. In this exemplary embodiment, the anode 100 is a composite structure of Ti/Al/Ti, a thickness of Ti is 20 nm and a thickness of Al is 70 nm. The cathode 300 may be made of an alloy material of Ag and Mg, wherein mass of Mg accounts for about 15% of total mass of the alloy; a thickness of the cathode is about 10 nm. The first functional layer 211 of the hole functional unit 210 has a doping subject of Bphen and a doping object of LiQ, with a doping ratio of about 10%. A thickness of the first functional layer 211 is about 20 nm. A material of the second functional layers 212 a and 212 b of the hole functional unit 210 is HATCN, and thicknesses of the second functional layers 212 a and 212 b are about 10 nm. The fourth functional layer 214 of the hole functional unit 210 has a doping subject of NPB and a doping object of HATCH, with a doping ratio of 1%. A thickness of the fourth functional layer 214 is about 10 nm. Materials of the third functional layers 213 a and 213 b and the hole transporting layer 230 of the hole functional unit 210 are all NPB, and total thickness of the third functional layers 213 a and 213 b and the hole transporting layer 230 is about 120 nm. For example, thicknesses of the third functional layers 213 a and 213 b are respectively about 20 nm, and a thickness of the hole transporting layer 230 is about 100 nm. A material of the electron blocking layer 240 is DBTPB, and a thickness of the electron blocking layer 240 is about 4 nm. A material of the light emitting layer 220 is MAND. DSA-Ph (5%), and a thickness of the light emitting layer 220 is about 20 nm. A material of the electron transporting layer 250 is Bphen, and a thickness of the electron transporting layer 250 is about 35 nm. A material of the electron injection layer 260 is Bphen doped with LiQ (the doping ratio is 10%), and a thickness of the electron injection layer 260 is about 80 nm. In this exemplary embodiment, the material of the hole transporting layer 230 is the same as the materials of the third functional layers 213 a and 213 b. The hole injection material used in the fourth functional layer 214 is the same as the materials of the second functional layers 212 a and 212 b, and the hole transport material used in the fourth functional layer 214 is the same as the materials of the third functional layers 213 a and 213 b. The material of the first functional layer 211 is the same as that of the electron injection layer 260.

In some exemplary embodiments, the OLED device includes a first electrode, a second electrode, and a first light emitting unit and at least one second light emitting unit stacked between the first electrode and the second electrode. The second light emitting unit is located between the first light emitting unit and the second electrode. Adjacent light emitting units are connected by a connection layer. The first light emitting unit and the second light emitting unit display different colors. The second light emitting unit includes a second light emitting layer and at least one of a hole injection layer, a hole transporting layer, an electron blocking layer, an electron transporting layer, an electron injection layer and a hole blocking layer. The first electrode may be an anode and the second electrode may be a cathode. In this exemplary embodiment, the OLED device is a tandem apparatus structure, and the first light emitting unit and at least one second light emitting unit share an anode and a cathode, which may improve the light emitting efficiency of the OLED device and prolong the service life of the OLED device. However, this is not limited in the present embodiment.

FIG. 12 is a schematic diagram of another structure of an OLED device according to at least one embodiment of the present disclosure. As shown in FIG. 12, the OLED device according to this exemplary embodiment includes an anode 100, a cathode 300, and a first light emitting unit 200 and two second light emitting units sequentially stacked between the anode 100 and the cathode 300. The first light emitting unit 200 is configured to emit light of a first color. The two second light emitting units include a light emitting unit 400 emitting a second color light and a light emitting unit 500 emitting a third color light. A connection layer is disposed between adjacent light emitting units. As shown in FIG. 12, a first connection layer 701 is disposed between the first light emitting unit 200 and the light emitting unit 400 emitting a second color light, which is configured to connect the first light emitting unit 200 and the light emitting unit 400 in series. A second connection layer 702 is disposed between the light emitting unit 400 emitting a second color light and the light emitting unit 500 emitting a third color light, which is configured to connect the light emitting units 400 and 500 in series to realize transfers of carriers. A structure of the first light emitting unit 200 may be referred to the description of the aforementioned embodiments, which will not be further illustrated here. In some examples, the light emitting unit 400 emitting a second color light may include a hole transporting layer, a light emitting layer, and an electron transporting layer which are sequentially stacked. The light emitting unit 500 emitting a third color light may include a hole transporting layer, a light emitting layer, and an electron transporting layer which are sequentially stacked. Since the OLED device of this exemplary embodiment includes the first light emitting unit 200 emitting a first color light, the light emitting unit 400 emitting a second color light, and the light emitting unit 500 emitting a third color light, the light finally emitted by the OLED device is mixed light. For example, the first light emitting unit 200 emits red light, the light emitting unit 400 emits green light, the light emitting unit 500 emits blue light, and the OLED device finally emits white light.

Table 1 is used to exemplarily show a comparison of light emitting performances of OLED devices with different structures. Table 1 illustrates light emission performances of the OLED devices in Comparative Example 2 and Example 2.

TABLE 1 Current Density Operating Light Emission (mA/cm2) Voltage (v) Efficiency (cd/A) Comparative 10 5.88 4.35 Example 2 Example 2 10 4.61 5.72

In order to facilitate comparison, a same basic structure is selected in both Comparative Example 2 and Example 2. For example, the structure shown in FIG. 9 is adopted in Example 2. A difference between the structure in Comparative Example 2 and the structure in Example 2 is that a hole functional unit is not included in the OLED device in Comparative Example 2, but a hole injection layer is disposed between the anode and the hole transporting layer.

In Comparative Example 2, an OLED device may be formed on a silicon-based substrate. The anode is a composite structure of Ti/Al/Ti, a thickness of Ti is 20 nm and a thickness of Al is 70 nm. The cathode is made of an alloy material of Ag and Mg, wherein mass of Mg accounts for about 15% of total mass of the alloy; a thickness of the cathode is about 10 nm. There is a hole injection layer (which is made of HATCN with a thickness of 10 nm), a hole transporting layer (which is made of NPB with a thickness of 150 nm), an electron blocking layer (which is made of DBTPB with a thickness of 4 nm), a light emitting layer (taking a blue light emitting layer as an example, which is made of MAND:DSA-Ph (5%) with a thickness of 20 nm), an electron transporting layer (which is made of Bphen with a thickness of 35 nm) and an electron injection layer (which is made of Bphen: LiQ(10%) with a thickness of 35 nm) in sequence between the anode and the cathode.

Materials and thicknesses of the substrate, the anode, the cathode, the electron blocking layer, the light emitting layer, the electron transporting layer and the electron injection layer in Example 2 are the same as those in Comparative Example 2.

In Example 2, there is a first functional layer (which is made of Bphen: Li (5%) with a thickness of 20 nm), a second functional layer (which is made of HATCN with a thickness of 10 nm), and a third functional layer (which is made of NPB with a thickness of 10 nm), a second functional layer (which is made of HATCN with a thickness of 10 nm), a third functional layer (which is made of NPB with a thickness of 10 nm), a hole transporting layer (which is made of NPB with a thickness of 80 nm), an electron blocking layer, a light emitting layer, an electron transporting layer and an electron injection layer in sequence between the anode and the cathode.

It may be seen from Table 1 that compared with the OLED device in Comparative Example 2, the operating voltage of the OLED device in Example 2 is significantly reduced, and the light emission efficiency is effectively improved.

FIG. 13 is a spectrum comparison diagram of Comparative Example 2 and Example 2. As shown in FIG. 13, compared with the OLED device in Comparative Example 2, the light emission intensity of the OLED device in Example 2 is effectively improved, and the peak position does not change.

In this exemplary embodiment, it is possible to overcome a difficulty of a hole injection due to the fact that a work function of the anode (for example, a work function of Ti is about 4.3 eV) does not meet the requirements (for example, a top-emitting silicon-based OLED requires the work function of the anode to be greater than 5 eV) by adding a hole functional unit between the anode and the hole transporting layer, thereby effectively reducing the operating voltage and power consumption of the OLED device and expanding a selection range of materials of the anode. In some examples, the OLED device of the present embodiment may be applied to a high-resolution silicon-based micro display devices, and an ultra-high resolution of more than 3000 Pixels Per Inch (PPI) may be achieved by adopting a Ti/Al/Ti anode.

A preparation method of an OLED device according to at least one embodiment of the present disclosure includes: forming a first electrode, a first light emitting unit and a second electrode on a substrate. An absorption rate of the first electrode for blue light is greater than an absorption rate of the first electrode for red light, and the absorption rate of the first electrode for blue light is greater than an absorption rate of the first electrode for green light. Forming of the first light emitting unit includes: sequentially forming a hole functional unit and a light emitting layer. Forming of the hole functional unit includes: forming at least two hole functional layers on a side of the first electrode away from the substrate; any hole functional layer at least includes a second functional layer for injecting holes and a third functional layer for transporting holes.

In some exemplary embodiments, the first electrode is in direct contact with the second functional layer of one hole functional layer in the hole functional unit.

In some exemplary embodiments, the hole functional unit further includes a first functional layer for transporting electrons in contact with the first electrode, and the first functional layer is located between the first electrode and the at least two hole functional layers. The first functional layer includes an electron transporting material doped with one or more of active metals and active metal compounds; an energy level difference between a LUMO energy level of the second functional layer and a HOMO energy level of the third functional layer is smaller than 1 eV.

In some exemplary embodiments, the hole functional layer further includes a fourth functional layer located between the second functional layer and the third functional layer, and the fourth functional layer is a mixed layer including a hole injection material and a hole transporting material. An energy level difference between a HOMO energy level of the hole transporting material of the fourth functional layer and a LUMO energy level of the second functional layer is smaller than 1 eV, and an energy level difference between the HOMO energy level of the hole transporting material of the fourth functional layer and a HOMO energy level of the third functional layer is smaller than 1 eV.

A preparation process of the OLED device of the present embodiment is illustrated below through an example.

In some examples, the preparation process of the OLED device includes: sequentially cleaning a transparent glass substrate forming an anode pattern in an ultrasonic environment of deionized water, acetone and absolute ethanol, and then drying it with nitrogen (N2) and treating it with oxygen (O2) plasma; then, placing the processed substrate in an evaporation chamber, and after a vacuum degree is lower than 5×10⁻⁴ Pa, sequentially depositing a first functional layer, a second functional layer, a third functional layer, a second functional layer, a third functional layer, a hole transporting layer, an electron blocking layer, a light emitting layer, an electron transporting layer, an electron injection layer and a cathode on a anode by vacuum thermal evaporation.

At least one embodiment of the present disclosure further provides a display substrate including the OLED device described above.

FIG. 14 is a schematic diagram of a display substrate according to at least one embodiment of the present disclosure. As shown in FIG. 14, the display substrate according to this exemplary embodiment includes: a substrate 10 and an OLED device 20 disposed on the substrate 10. The OLED device 20 is the OLED device provided in the foregoing embodiments In some examples, the substrate 10 may be a silicon substrate. The display substrate may be a silicon-based OLED substrate with a top emitting structure. However, this is not limited in the present embodiment.

FIG. 15 is a schematic diagram of a display apparatus according to at least one embodiment of the present disclosure. As shown in FIG. 15, the present embodiment provides a display apparatus 91, which includes a display substrate 910. The display substrate 910 is the display substrate provided in the forgoing embodiments. In some examples, the display substrate 910 may be a silicon-based OLED substrate. The display apparatus 91 may be: augmented reality (AR) or virtual reality (VR) products, mobile phones, tablet computers, televisions, monitors, laptops, digital photo frames, navigators, and any other products or components with display functions. However, this is not limited in the present embodiment.

The drawings in the present disclosure only refer to the structures involved in the present disclosure, and common designs may be referred to for other structures. The embodiments of the present disclosure and the features in the embodiments may be combined with each other to obtain a new embodiment if there is no conflict.

Those of ordinary skills in the art should understand that modifications or equivalent substitutions may be made to the technical solutions of the present disclosure without departing from the spirit and scope of the technical solutions of the present disclosure, all of which should be included within the scope of the claims of the present disclosure. 

What is claimed is:
 1. An OLED device, comprising: a first electrode, a second electrode, and a first light emitting unit located between the first electrode and the second electrode, wherein an absorption rate of the first electrode for blue light is greater than an absorption rate of the first electrode for red light, and the absorption rate of the first electrode for blue light is greater than an absorption rate of the first electrode for green light; the first light emitting unit comprises a light emitting layer and a hole functional unit located between the first electrode and the light emitting layer; and the hole functional unit comprises at least two hole functional layers, and any hole functional layer comprises a second functional layer for injecting holes and a third functional layer for transporting holes which are stacked along a direction away from the first electrode.
 2. (canceled)
 3. The OLED device of claim 1, wherein a difference between a lowest unoccupied molecular orbital (LUMO) energy level of the second functional layer adjacent to the first electrode and a work function of the first electrode is smaller than 1.6 eV. 4-5. (canceled)
 6. The OLED device of claim 1, wherein, the first electrode is in direct contact with the second functional layer of one of the hole functional layers.
 7. The OLED device of claim 1, wherein, a thickness of the second functional layer is smaller than a thickness of the third functional layer.
 8. The OLED device of claim 1, wherein a thickness of the second functional layer in the hole functional layer close to the first electrode in the hole functional unit is smaller than a thickness of the second functional layer in the hole functional layer away from the first electrode in the hole functional unit.
 9. The OLED device of claim 1, wherein a thickness of the third functional layer in the hole functional layer close to the first electrode in the hole functional unit is smaller than a thickness of the third functional layer in the hole functional layer away from the first electrode in the hole functional unit.
 10. (canceled)
 11. The OLED device of claim 1, wherein the light emitting layer comprises a first light emitting layer, a second light emitting layer and a third light emitting layer which are sequentially stacked along the direction away from the first electrode, wherein the first light emitting layer and the second light emitting layer are in direct contact with each other, and a connection layer is disposed between the second light emitting layer and the third light emitting layer.
 12. The OLED device of claim 11, wherein the first light emitting layer is a red light emitting layer, the second light emitting layer is a green light emitting layer, and the third light emitting layer is a blue light emitting layer.
 13. The OLED device of claim 1, wherein the hole functional unit further comprises a first functional layer for transporting electrons, wherein the first functional layer is located between the first electrode and the at least two hole functional layers, and the first functional layer is in contact with the first electrode; the first functional layer comprises an electron transporting material doped with one or more of active metals and active metal compounds; and an energy level difference between a lowest unoccupied molecular orbital (LUMO) energy level of the second functional layer and a highest occupied molecular orbital (HOMO) energy level of the third functional layer is smaller than 1 electron volt eV. 14-17. (canceled)
 18. The OLED device of claim 13, wherein the hole functional layer further comprises a fourth functional layer located between the second functional layer and the third functional layer, wherein the fourth functional layer is a mixed layer comprising a hole injection material and a hole transporting material; an energy level difference between a HOMO energy level of the hole transporting material of the fourth functional layer and the LUMO energy level of the second functional layer is smaller than 1 eV, and an energy level difference between the HOMO energy level of the hole transporting material of the fourth functional layer and the HOMO energy level of the third functional layer is smaller than 1 eV. 19-20. (canceled)
 21. The OLED device of claim 13, wherein the first functional layer comprises a first material layer in contact with the first electrode and a second material layer between the first material layer and the hole functional layer; the first material layer comprises a metal material, and the second material layer comprises an electron transporting material doped with one or more of an active metal and an active metal compound.
 22. The OLED device of claim 1, wherein the first light emitting unit further comprises at least one of: a hole transporting layer between the hole functional unit and the light emitting layer, an electron blocking layer between the light emitting layer and the hole transporting layer, an electron blocking layer between the light emitting layer and the hole functional unit, an electron transporting layer between the light emitting layer and the second electrode, an electron injection layer between the electron transporting layer and the second electrode, and a hole blocking layer located between the light emitting layer and the electron transporting layer.
 23. The OLED device of claim 1, further comprising: one or more second light emitting units located between the first light emitting unit and the second electrode; wherein adjacent light emitting units are connected through a connection layer; the first light emitting unit and the second light emitting unit emit light with different colors; and at least one of the second light emitting units comprises a light emitting layer and at least one of a hole injection layer, a hole transporting layer, an electron blocking layer, an electron transporting layer, an electron injection layer and a hole blocking layer.
 24. The OLED device of claim 1, wherein the first electrode is a reflective anode and the second electrode is a light-transmitting cathode.
 25. A display substrate, comprising the OLED device of claim
 1. 26. A display apparatus, comprising the display substrate of claim
 25. 27. A preparation method for an OLED device, comprising: forming a first electrode, a first light emitting unit and a second electrode on a substrate; wherein an absorption rate of the first electrode for blue light is greater than an absorption rate of the first electrode for red light, and the absorption rate of the first electrode for blue light is greater than an absorption rate of the first electrode for green light; and forming the first light emitting unit, which comprises sequentially forming a hole functional unit and a light emitting layer; wherein forming the hole functional unit comprises forming at least two hole functional layers on a side of the first electrode away from the substrate, and any hole functional layer comprises a second functional layer for injecting holes and a third functional layer for transporting holes which are stacked along a direction away from the first electrode.
 28. The preparation method of claim 27, wherein the first electrode is in direct contact with the second functional layer of one of the hole functional layers in the hole functional unit.
 29. The preparation method of claim 27, wherein the hole functional unit further comprises a first functional layer for transporting electrons in contact with the first electrode, wherein the first functional layer is located between the first electrode and the at least two hole functional layers; and the first functional layer comprises an electron transporting material doped with one or more of active metals and active metal compounds; an energy level difference between a lowest unoccupied molecular orbital (LUMO) energy level of the second functional layer and a highest occupied molecular orbital (HOMO) energy level of the third functional layer is smaller than 1 eV.
 30. The preparation method of claim 29, wherein the hole functional layer further comprises a fourth functional layer located between the second functional layer and the third functional layer, the fourth functional layer is a mixed layer comprising a hole injection material and a hole transporting material; and an energy level difference between a HOMO energy level of the hole transporting material of the fourth functional layer and the LUMO energy level of the second functional layer is smaller than 1 eV, and an energy level difference between the HOMO energy level of the hole transporting material of the fourth functional layer and the HOMO energy level of the third functional layer is smaller than 1 eV. 